The invention relates to connecting elements for mechanical transmissions and in particular to shaft couplings.
Shaft couplings in which a resilient member is provided between the driving and driven parts (hubs) of the coupling are known and widely used. Since small size and low values of weight and rotary inertia are frequently of critical importance, and since smaller couplings are usually less costly, spider or jaw couplings are quite popular. It is known (e.g., see E. Rivin, xe2x80x9cDesign and Application Criteria for Connecting Couplingsxe2x80x9d, in ASME Journal of Mechanisms, Transmissions, and Automation in Design, 1986, Vol. 108, No. 1, pp. 96-105) that the spider couplings have the smallest size and the lowest weight and rotary inertia for a given rated torque. However, they also possess the highest values of torsional stiffness as well as radial stiffness which is important for misalignment compensation (see the quoted paper). Thus, spider couplings of conventional designs provide a poor isolation of torsional vibrations and also poor compensation of forces on bearings of the connected shafts due to inevitable shaft misalignments. In addition, the high stiffness values result in very small damping contribution of the spider coupling to the transmission system, while damping enhancement in the transmission system is often highly desirable. Since spider couplings are usually equipped with elastomeric flexible elements, they cannot be used in high temperature and other aggressive environments, as well as in the environments wherein special non-contamination and sanitary requirements are specified (e.g., in food and cosmetics processing machinery).
Another shortcoming of the conventional spider couplings is relatively fast deterioration of the elastomeric spider due to stress concentrations in the sharp corners of the spider legs, usually having rectangular cross sections.
While the issues of excessive torsional and misalignment compensation stiffness, as well as the issue of stress concentration had been addressed in our U.S. Pat. No. 4,557,703, the issues of applicability in the extreme environments were not. There are known cases when spiders are fabricated from a material acceptable in the extreme environments, such as bronze, but use of such spiders results in even higher torsional and compensation stiffness values.
The present invention addresses the shortcomings of the conventional spider couplings by providing a coupling which, while maintaining the advantageous small size and small weight characteristics, can be used in aggressive or contamination-sensitive environments, has reduced torsional and compensation stiffness, may possess a significant damping and also may positively influence the damping characteristics of the transmission system wherein the subject coupling is installed.
Some embodiments of the present invention can be retrofitted into existing installations of the spider couplings without replacement of the already installed hubs. There is also a possibility of fine tuning of the coupling characteristics with the same hubs in place.
This invention is directed to an improved form of connecting coupling for mechanical assemblies, especially for power transmission shafts. Broadly, the invention involves using a spider made from metal or from other rigid material, in which the load-carrying xe2x80x9clegsxe2x80x9d of the spider are shells of revolution of a tapered, barrel, or cylindrical shape. These shells can be solid or wound from wire in a manner of helical coil springs. These legs are attached by mechanical means to the holding base of the spider (centrally or peripherally situated), while being capable to freely deform under radial loading by tangential forces transmitted by the coupling, as well as under axial loading by forces radial to the coupling and generated due to misalignment of the connected shafts. When even larger deformations are desirable, the shells can be generated by coiling them from wire, like helical coil springs.
Even greater deformations can be achieved if the wire made from a superelastic alloy is used for coiling the shells.
The radially deformable shells of revolution can accommodate large tangential forces in torque-transmitting couplings. Deformations of the shells (thus, torsional stiffness of the coupling) can be adjusted or tuned by varying wall thickness of the deformable shells, with increase of maximum deformation (thinner walls or thinner wire in the wound shells) being accompanied by reduction of the rated torque of the coupling.
The shells are attached to and are held together by the holding base, either a centrally located xe2x80x9ccentral basexe2x80x9d to which the shells of revolution are connected as spider legs, or a ring surrounding the coupling to which the shells are connected in a similar way. The latter embodiment allows replacement of the xe2x80x9cspiderxe2x80x9d without a need to disassemble the whole setup, e.g. consisting of a motor driving a hydraulic pump.
The shells are attached to the holding base in such a way that they cannot separate from the base (are xe2x80x9ccaptivexe2x80x9d), while having some relative mobility thus allowing free deformation of each loaded shell.